The role of cytochrome P450 monooxygenase in the different responses to fenoxaprop-P-ethyl in annual bluegrass (Poa annua L.) and short awned foxtail (Alopecurus aequalis Sobol.)

• Poa annua and Aolopecurus aequalis were tolerant and sensitive to fenoxaprop-P-ethyl, respectively.
• The method for isolating the microsome from weeds had been established.
• The activity of fenoxaprop-P-ethyl could be synergized by PBO in P. annua, but not malathion.
• The contents and activities of cyt P450 could be inducted in P. annua by fenoxaprop-P-ethyl.

Herbicide resistance or tolerance in weeds mediated by cytochrome P450 monooxygenase is a considerable problem. However, cytochrome P450 mediated resistance or tolerance in weeds was less studied. Thus, in this work, the role of the cytochrome P450 monooxygenase in the different responses of Poa annua and Alopecurus aequalis to fenoxaprop-P-ethyl was studied. We found that the effect of fenoxaprop-P-ethyl could be synergized by piperonyl butoxide (PBO) in P. annua, but not by malathion. After being treated with fenoxaprop-P-ethyl (containing mefenpyr-diethyl), the contents of cytochrome P450 and cytochrome b5 in P. annua increased significantly compared to plants treated with mefenpyr-diethyl only or untreated plants. However, the increase was less in A. aequalis, which was susceptible to fenoxaprop-P-ethyl. The activities of ρ-nitroanisole O-demethylase (PNOD), ethoxyresorufin O-deethylase (EROD), ethoxycoumarin oxidase (ECOD) and NADPH-dependent cytochrome P450 reductase mediated by cytochrome P450 monooxygenase increased in P. annua after treatment with fenoxaprop-P-ethyl, especially the activities of ECOD and cytochrome P450 reductase. Besides this, cytochrome P450 monooxygenase activity toward fenoxaprop-P-ethyl in P. annua increased significantly compared to untreated or treated with mefenpyr-diethyl plants and treated or untreated A. aequalis. Cytochrome P450 monooxygenase may play an important role in the different responses to fenoxaprop-P-ethyl in P. annua and A. aequalis.

The changes in PNOD (a), EROD (b), ECOD (c) and NADPH-cytochrome P450 reducase (d), mediated by cytochrome P450 monooxygenase, fenoxaprop-P- ethyl (41.4 g ai·ha−1, containing mefenpyr-diethyl) or mefenpyr- diethyl (11.4 g ai·ha−1) treatment compared with untreated weed. The activities of PNOD, EROD, ECOD and NADPH-cytochrome P450 reducase were 1.46, 0.06, 1.98 × 10−3, 1.07 nmol·min−1mg−1 protein in the untreated P. annua, and 1.44, 0.07, 1.40 × 10−3, 1.43 nmol·min−1mg−1 protein respectively. Poa + F: Poa annua treated with fenoxaprop-P-ethyl (containing mefenpyr-diethyl); Ala + F: Alopecurus aequalis treated with fenoxaprop-P-ethyl (containing mefenpyr-diethyl); Poa + M: P. annua treated with mefenpyr-diethyl and Ala + M: A. aequalis treated with mefenpyr-diethyl.Figure optionsDownload as PowerPoint slide